THE   UNIVERSITY 

OF   ILLINOIS 

LIBRARY 


G-50.1 


.-2. 


T\       V  A 


UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  194 


A  NEW  LIMESTONE  TESTER 


BY  CYKIL  G.  HOPKINS 


URBANA,  ILLINOIS,  JANUARY,  1917 


LIMESTONE  TESTER 

(Weight,  about  40  grams.    Capacities  below  connecting 
tube,  about  35  cc.  and  50  cc.  respectively) 


A  NEW  LIMESTONE  TESTER 

BT  CYRIL  G.  HOPKINS,  CHIEF  IN  AGRONOMY  AND  CHEMISTRY 

Since  the  publication  of  Circular  185,  describing  a  limestone 
tester,  the  writer  has  designed  a  more  simple  apparatus  by  means  of 
which  the  purity  of  limestone  can  be  quickly  ascertained  with  a  very 
satisfactory  degree  of  accuracy. 

As  shown  in  the  accompanying  illustration,  this  tester  consists 
of  two  small  glass  bottles,  joined  together  and  fitted  with  ground-glass 
stoppers,  the  stopper  of  the  smaller  bottle  resting  upon  a  surface  only 
slightly  inclined  from  the  horizontal,  and  projecting  loosely  into  the 
neck.  A  set  of  weights  from  5  milligrams  to  50  grams,  a  balance  suit- 
able for  these  weights  with  a  capacity  of  100  grams,  a  thermome£er,  a 
25  cubic  centimeter  graduated  cylinder,  and  the  limestone  tester,  are 
all  one  needs  for  testing  limestone  for  relative  purity. 

To  make  the  test,  place  5  grams  of  pulverized  limestone  in  the 
larger  bottle  and  fill  the  smaller  one  to  the  side-opening  with  acid 
made  by  mixing  about  equal  parts  of  concentrated  hydrochloric  acid 
and  water  and  saturating  with  carbon  dioxid.  Insert  the  stoppers  and 
weigh.  Now  tip  the  apparatus  carefully  until  the  acid  begins  to  flow 
thru  the  side-opening.  As  it  drops  upon  the  limestone,  the  carbonate 
is  changed  to  chlorid  and  the  liberated  carbon  dioxid  gas  passes  thru 
the  side-opening,  lifting  the  small  stopper  as  it  passes  out.  Partly 
immerse  the  apparatus  in  cool  water  to  keep  it  at  about  room  tempera- 
ture. Gradually  transfer  the  acid  until  foaming1  ceases;  then  dry 
the  apparatus  with  a  soft  cloth,  weigh,  and  note  the  loss.  To  this  loss 
in  weight  add  .6  milligram  for  each  cubic  centimeter  of  air-space  in 
the  "loaded"  apparatus,  then  deduct  the  proper  percentage  for  the 
room  temperature  (about  1  percent  for  70°  F. — see  Table  1),  and 
divide  by  2.2  to  get  the  relative  purity  of  the  stone. 

If  the  direct  loss  represented  only  the  total  carbon  dioxid  liber- 
ated, then  its  weight  divided  by  2.2  would  give  the  relative  purity  of 
the  stone  in  terms  of  calcium  carbonate,  since  5  grams  of  pure  calcium 
carbonate  (CaC03)  contains  2.2  grams  of  carbon  dioxid  (C02),  the 
atomic  weights  being  40  for  calcium,  12  for  carbon,  and  16  for  oxygen. 

However,  the  moist  air  which  fills  the  air-space  at  the  beginning 
is  replaced  by  moist  carbon  dioxid  during  the  reaction.  At  70°  Fah- 
renheit (21°  centigrade)  and  29.33  inches  (745  millimeters)  barometric 

'Too  persistent   frothing  may  be  prevented  by  adding  a  few  drops  of  gas- 
engine  cylinder  oil  to  the  acid  before  weighing  the  "loaded"  apparatus. 

487 


488  BULLETIN  No.  194  [January, 

pressure  (taken  as  room  temperature  and  average  atmospheric  pres- 
sure at  an  elevation  of  600  feet  above  sea  level),  1  cubic  centimeter 
contains  1.744  milligrams  of  carbon  dioxid  or  1.148  milligrams  of  air, 
not  including  the  water  vapor.  The  difference  in  weight  is  practically 
.6  milligram  per  cubic  centimeter;  and,  if  the  air-space  in  the 
"loaded"  apparatus  is,  for  example,  75  cubic  centimeters,  then  45 
milligrams  should  be  added  to  the  loss  in  weight,  under  these  condi- 
tions. 

Again,  the  gas  (air  or  carbon  dioxid)  passing  out  of  the  appa- 
ratus during  the  reaction  is  accompanied  by  some  water  vapor,  which 
amounts  to  .018  milligram  per  cubic  centimeter  at  70°  F.  The  com- 
bined weight  of  the  carbon  dioxid  and  water  vapor  in  1  cubic  centi- 
meter, at  70°  F.  and  29.33  inches,  is  1.762  milligrams  (1.744  +  .018). 
Thus,  about  1  percent  must  be  deducted  from  the  first  corrected  weight. 

For  example,  5  grams  of  a  certain  limestone  shows  a  loss  of  1.990 
grams.  The  first  correction  (45  milligrams)  increases  this  to  2.035 
grams,  and  the  second  correction  (20  milligrams)  reduces  it  to  2.015 
grams.  This  divided  by  2.2  gives  .916,  or  91.6  percent,  as  the  relative 
purity  of  the  stone. 

For  all  practical  purposes,  the  first  correction  is  a  constant  for 
each  apparatus,  the  variations  for  ordinary  differences  in  temperature 
and  pressure  being  negligible.  The  second  correction  varies  appre- 
ciably only  with  change  of  temperature.  For  each  2  degrees  above 
70°,  the  correction  of  1  percent  is  increased  by  about  .1  percent.  Thus, 
if  the  room  temperature  is  86°,  add  to  the  weight  of  escaped  gas  .6 
milligram  per  cubic  centimeter  of  air-space  and  then  deduct  1.74  per- 
cent (see  Table  1).  This,  in  the  above  example,  with  a  direct  loss  of 
1.900  grams,  would  give  a  final  corrected  weight  of  2.000  grams  of 
carbon  dioxid  from  5  grams  of  stone,  and  this  divided  by  2.2  gives 
90.9  percent.  But  to  perform  the  operation  at  86°  and  figure  the  sec- 
ond correction  at  1  percent,  as  should  be  done  for  70°,  would  intro- 
duce an  error  of  .7  percent  in  the  purity  found. 

To  saturate  the  hydrochloric  acid  with  carbon  dioxid,  drop  a  piece 
of  limestone  weighing  3  or  4  grams  into  a  pint  bottle  of  the  diluted 
acid,  replacing  the  stopper  after  foaming  ceases. 

To  determine  the  air-space  in  the  "loaded"  apparatus,  place  5 
grams  of  pulverized  limestone  in  the  larger  bottle,  fill  the  smaller 
bottle  to  the  side-opening  with  water,  and  then  pour  in  measured 
water  from  a  graduated  cylinder  and  note  the  addition  .required  to 
completely  fill  the  apparatus. 

If  one  has  a  barometer,  and  a  balance  capable  of  weighing  to  1 
milligram,  a  still  higher  degree  of  accuracy  may  be  secured  by  using 
the  data  given  in  the  accompanying  tables. 

Thus,  5  grams  of  pulverized  limestone  shows  a  direct  loss  of  2.164 
grams  at  77°  and  28.50  inches,  with  an  apparatus  having  71  cubic 
centimeters  air-space  when  "loaded."  When  saturated  with  water 


1917] 


489 


TABLE  1. — CARBON  DIOXID  SATURATED  WITH  WATER  VAPOR  AT 
760  MILLIMETERS   (29.92  INCHES) 


Temperature 

Milligrams  per  cubic  centimeter 

Percent 
of  water 
in  total 

Pressure  of 
water  vapor 
millimeters 

°C 

°F 

Carbon 
dioxid 

Water 
vapor 

Total 

10 

50.0 

1.879 

.009 

1.888 

.50 

9.2 

11 

51.8 

1.870 

.010 

1.880 

.53 

9.8 

12 

53.6 

1.862 

.011 

1.872 

.57 

10.5 

13 

55.4 

1.853 

..Oil 

1.864 

.61 

11.2 

14 

57.2 

1.844 

.012 

1.856 

.65 

11.9 

15 

59.0 

1.836 

.013 

1.848 

.69 

12.7 

16 

60.8 

1.827 

.013 

1.840 

.73 

13.5 

17 

62.6 

1.818 

.014 

1.832 

.78 

14.4 

18 

64.4 

1.809 

.015 

1.824 

.83 

15.4 

19 

6G.2 

1.800 

.016 

1.816 

.89 

16.3 

20 

68.0 

1.791 

.017 

1.808 

.95 

17.4 

21 

69.8 

1.782 

.018 

1.800 

1.01 

18.5 

22 

71.6 

1.773 

.019 

1.792 

1.08 

19.7 

23 

73.4 

1.763 

.020 

1.784 

1.15 

20.9 

24 

75.2 

1.754 

.022 

1.773 

1.22 

22.2 

25 

77.0 

1.744 

.023 

1.767 

1.29 

23.6 

26 

78.8 

1.735 

.024 

1.759 

1.37 

25.0 

27 

80.6 

1.725 

.026 

1.751 

1.46 

26.5 

28 

82.4 

1.715 

.027 

1.742 

1.55 

28.1 

29 

84.2 

1.705 

.029 

1.734 

1.64 

29.8 

30 

86.0 

1.695 

.030 

1.725 

1.74 

31.5 

31 

87.8 

1.685 

.032 

1.716 

1.85 

33.4 

32 

89.6 

1.674 

.033 

1.707 

1.96 

35.4 

33 

91.4 

1,664 

.035 

1.609 

2.08 

37.4 

34 

93.2 

1.653 

.037 

1.690 

2.20 

39.6 

35 

95.0 

1.643 

.039 

1.682 

2.34 

41.8 

vapor  under  those  conditions,  1  cubic  centimeter  contains  1.659  milli- 
grams of  carbon  dioxid  or  1.093  milligrams  of  air,  the  difference  being 
.566  milligrams,  or  40  milligrams  in  71  cubic  centimeters.  This  first 
correction  being  added  gives  2.204  grams  of  moist  carbon  dioxid,  of 
which  1.29  percent,  or  28  milligrams,  is  water  vapor,  leaving  2.176 
milligrams  of  dry  carbon  dioxid,  and  this  divided  by  2.2  gives  98.9 
percent;  whereas,  if  the  barometric  pressure  were  assumed  to  be  29.33 
inches,  the  purity  found  would  be  99.0  percent,  as  may  readily  be 
computed  from  the  data  given  in  Tables  1,  2,  and  3. 

NOTE. — This  method  of  testing  for  relative  strength  or  purity  serves  to  meas- 
ure the  basicity  (power  to  neutralize  acidity)  of  dolomitic  as  well  as  of  the  more 
common  limestone,  but  to  hasten  the  reaction  it  is  well  to  pulverize  dolomite  so  it 
will  pass  thru  a  100-mesh  sieve. 


490 


BULLETIN  No.  194 


[January, 


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BULLETIN  No.  194 


[January, 


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A  NEW  LIMESTONE  TESTER 


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494  BULLETIN  No.  194  [January, 

LIMESTONE  SAMPLES 

In  collecting  limestone  for  analysis,  care  should  be  taken  to  secure 
a  sample  which  will  fairly  represent  the  stone,  because  even  an  accu- 
rate analysis  does  not  tell  the  whole  truth  if  an  imperfect  sample  is 
analyzed.  To  sample  a  stratum  of  stone  it  is  well  to  chip  off  small 
pieces  every  few  inches  from  top  to  bottom.  If  about  the  same  amount 
is  taken  from  each  point,  the  composite  will  represent  the  stratum. 
If  two  or  more  strata  exist  and  it  is  desired  to  know  the  relative  purity 
of  each,  then  a  separate  composite  sample  should  be  taken  from  each 
stratum. 

It  should  be  kept  in  mind  that  samples  taken  from  natural  ex- 
posures, or  rock  outcrops,  may  not  fairly  represent  the  unweathered 
stone.  As  a  rule,  calcium  carbonate  is  more  readily  soluble  in  rain 
water  than  are  the  impurities  which  may  be  associated  with  it  in  the 
natural  stone,  and  consequently  the  weathered  outcrop  may  contain 
a  lower  percentage  of  carbonate. 

In  collecting  a  sample  from  a  carload  of  pulverized  limestone, 
twenty  or  more  small  portions  should  be  taken  from  different  places 
an«i  different  depths,  and  these,  aggregating  one  or  two  pounds,  should 
be  well  mixed  for  the  composite  sample.  Practically  all  limestone  de- 
posits contain  strata  which  differ  more  or  less  in  relative  purity,  and 
it  is  easily  possible  that  the  last  1,000  pounds  of  pulverized  limestone 
loaded  into  a  car  may  have  come  from  a  stratum  whose  composition  is 
appreciably  better  or  poorer  than  the  average.  Of  course  the  stone 
migL  vary  even  by  carload  lots,  and  no  source  of  limestone  should  be 
condemned,  or  even  discriminated  against,  because  one  carload  has 
been  found  ' '  off  grade. ' ' 

The  purest  limestone  is  not  always  the  most  economical  to  use. 
Thus  it  is  better  to  apply  stone  of  80  percent  purity  costing  $1.50  a 
ton  spread  on  the  land,  than  stone  of  98  percent  purity  costing  $2, 
equal  fineness  being  assumed. 

For  use  in  soil  improvement,  the  limestone  need  not  be  very  finely 
ground,  but  it  should  include  all  of  the  fine  dust  produced  in  the  proc- 
ess of  crushing  or.  grinding.  At  least  four  important  factors  are 
involved  in  the  question  of  fineness :  cost  of  production,  cost  of  appli- 
cation, durability,  and  availability.  Stone  ground  to  pass  thru  a  10- 
mesh  sieve  (100  holes  per  square  inch)  costing  $2  a  ton  spread  on  the 
land  is  more  expensive  than  stone  with  only  75  percent  of  10-mesh 
at  $1.50  a  ton,  because  the  stone  which  is  coarser  than  10-mesh  costs 
nothing,  relatively,  and  it  has  some  value.  Its  value  may  be  even 
greater  than  that  of  an  equal  weight  of  the  finer  stone,  when  measured 
solely  by  its  effects  after  the  second  or  third  year. 

It  costs  less  to  spread  three  tons  of  limestone  at  one  application 
than  to  spread  them  in  six  annual  applications  of  1000  pounds  each. 
If  three  tons  are  applied  every  six  years,  the  finer  material  is  needed 


1917]  A  NEW  LIMESTONE  TESTER  495 

for  quick  availability,  and  the  coarser  may  be  equally  important  to 
provide  for  durability  of  benefit.  Investigations  now  in  progress  will 
ultimately  furnish  more  information  in  regard  to  this  question  of  fine- 
ness. From  the  information  thus  far  secured,  it  is  conceivable  that 
limestone  ground  so  that  90  percent  will  pass  thru  a  4-mesh  sieve  (16 
holes  per  square  inch)  and  50  percent  thru  a  10-mesh  may  prove  as 
economical  as  any  for  use  in  permanent  rational  systems  of  soil  im- 
provement. 

COST  OF  LIMESTONE  TESTER 

The  cost  of  an  outfit  for  testing  limestone  as  described  herein  is 
less  than  $10.  This  includes  the  tester  shown  on  the  second  page,  a 
balance,  a  set  of  weights,  a  forceps  for  handling  the  weights,  a  mortar 
and  pestle  for  pulverizing  the  stone,  a  25  cubic  centimeter  graduated 
cylinder  to  be  used  for  measuring  the  air  space  in  the  tester  and  use- 
ful also  in  transferring  acid  to  the  apparatus,  and  a  spatula  for  placing 
the  pulverized  stone  on  the  balance  pan.  (After  weighing,  the  5 
grams  of  stone  may  be  poured  onto  a  small  square  of  clean  paper,  pre- 
viously creased,  and  from  this  poured  into  the  tester,  which  should 
stand  on  a  larger  piece  of  clean  paper,  so  that  if  any  stone  is  spilled 
it  can  be  recovered.) 

The  Illinois  Experiment  Station  will  be  glad  to  assist  anyone 
desiring  to  secure  this  outfit.  (Strong  hydrochloric  acid  can  be  se- 
cured from  drug  stores,  and  thermometers  are  already  present  in  most 
homes  and  offices.) 


UNIVERSITY  OF  ILLINOIS-URBANA 


